Radio receiving system



Sept. 12, 1933,

s. w. PLACE 1,926,173

RADIO RECEIVING SYSTEM Filed Jan. 21, 1931 IN V EN TOR.

ATTORNEY.

Patented Sept. 12, 1933 FFEE 1,926,173 RADIO RECEIVING SYSTEM Samuel W.Place, Norristown, Pa., assignor to Atwater Kent Manufacturing Company,Philadelphia, Pa., a corporation of Pennsylvania Application January 21,1931. Serial No. 510,149 16 Claims. (Cl. 25020) My invention relates toradio receiving systems, particularly those involving amplification bythermionic tubes of the screen or shield grid type for amplification ofradio frequency energy in one or more stages;

In accordance with my invention there is effected, by adjustment of asingle device, more specifically a single contact or brush a resistanceor potentiometer, variation of the amplification by one or moreamplifier tubes of 1 upon or of the aforesaid screen grid type, byvariation of screen grid voltage or bias to vary t cation factor of thetube or tubes, with simultaneous variation of the magnitude of transferof radio frequency signal energy to said tube or tubes, or from oneormore of succeeding tube or tubes.

My invention resides in a method them to a and apparatus of thecharacter hereinafter described'and claimed.

For an understanding of my inv ention and for an illustration of some ofthe forms it may take, reference is to be had to the accompanyingdrawing, in which:

Fig. 1 is adiagrammatic view of receiving apparatus embodying a stage ofradio frequency amplification, and utilizable for pra 'formof myinvention;

Fig, 2 is a diagrammatic View of a cticing one erodyne radio receivingsystem embodying a further form of my invention.

absorbs the electro-radiant energy from a natural medium. Through acondenser K, which is antenna system and at the same time to provide alow reactance path for the incoming radio frequency energy, the antennaA is con,-

' nected to the contact or brush 1 movable along the resistance R, whoseone terminal connects through a stopping condenser K1 with one terminalof the primary 1? of a radio frequency transformer T, and whose otherend connects with the other terminal of the primary P. The

second terminal of the resistance R a nd primary P connects to earth orcounter capacity E through the resistance R1; and to the cathode c ofamplifier tube V of the screen grid type. The cathode is, which may bean incandescent filament or a cathode raised in temperature by a heater,is connected to ground or earth through a condenser K2, of lowvreactance for radio frequency current, in shunt to the resistance R1;

superhetupon the potentiometer resistance R. utilized tokeep the directcurrent voltage off the 7 Connected across the terminals of thesecondary S of the transformer T is the variable tuning condenser C fortuning the input circuit of thetube V to the various radio frequenciesof a suitable range, for example, to tune to the broadcast frequenciesnow commonly employed. One terminal of the tunable loop SC is connectedto the control grid g of the tube V while its other terminal isconnected to earth or, in effect, to the cathode lc' through thecondenser K2. In" the grid'lead may be inserted a damping resistance T,which generally may be omitted, though of advantage in event of feedbackor regenera- 7 tion through capacity, generally substantially entirelyexternal to the tube V exising between theplate or anode a and the gridg. v,

The positive treminal 2, of the B source, not shown, or source ofuni-directional or direct current for supplying the anode or platecircuit of the tube V, is connected to one terminal of the resistance R,while its other terminal is connected to ground E. Current accordinglyflows from theB source through the resistances R and R1 in series. Fromthe contact or brush 1, there is a connection to the screen grid orshield grid s through aradio frequency choke coil 3; and from a pointbetween the coil 3 and the screen grid 3 there is a connection to groundE through the condenser K3, exhibiting low reactance for currents of theradio frequency range involved.

The positive potential impressed upon the screen or shield grid sof thetube V is varied as the contact 1 is moved to diiferent positions Themovement of the contact or brush 1 along the resistance R has thefurther and simultaneous effect of varyinglthe amount of the receivedradio frequency or signal-representing energy impressedupon thetransformer primary P, and thence upon the input of the tube V..

As the brush or contact 1 is moved downwardly along the resistance R theamplitude of the received radio frequency or signal representing energyimpressed upon the input of the tube V is reduced;and'simultaneously'the positive po.-

tential or bias of the screen grid s is reduced,

causing in effect a reduction in the" magnitude of the amplificationfactor of thetube V thereby diminishing the amplification of the radiofrequency energy, and thereby-reducing the amount of signal-representingor radio frequencyenergy impressed upon the succeeding circuit, not

shown, through any suitable coupling means generically represented bythe transformer primary P1.

The signal representing energy transferred by the coupling, representedby the coupling Pl, may then be further amplified if desired; impressedupon a demodulator or detector, and the audio frequency current in theoutput of I the detector then may be amplified by one or more amplifiertubes and impressed upon .a. signal translating instrument such as aloud speaker.

If the volume is controlled only by reduction of the positive bias onthe screen grid, and carried to an extent Where the positive potentialof the screen grid is reduced to substantially zero, the plate currentis also reduced to substantially zero; Under such circumstances incomingradio frequency energy, having great modulation, will nevertheless causesome plate current to flow on strong signals while little or no platecurrent will flow with weak signals. Large and serious distortion willresult when such reat reduction of volume is effected solely byreduction of screen grid potential. a

- To overcome the foregoing difiiculty, it has been proposed to apply asecond and independent volume control which reduces the amount of theradio frequency signal-representing energy transferred from the antennaor impressed upon the radio frequency amplifier, or which reduces theamount of radio frequency signal-representing energy transferred fromone vacuum tube amplifier to another vacuum tube of or within the radioreceiving system; and it has been proposed to effect the separatecontrols of screen grid bias and transfer of radio frequencysignalrepresenting energy by operating their adjustable elementsmechanically ,in unison.

In accordance with my invention, however, the two electrical efiects areaccomplished by one andthe same electrical devicejsuch as a singlepotentiometer or adjustable resistance.

As the brush or contact 1 is moved from the upper toward the lower endof the resistance R, its effect, in reducing the amount of radiofrequency signal-representing energy impressed upon the input circuit ofthe tube V, is at first small, and then becomes rapidly greater andgreater, thereby more rapidly decreasing the signal-representing voltageimpressed upon the input of the tube V, and therefore the volume,

as the contact 1 approaches the lower end of the resistance R,

The combined action, therefore, is such that as the contact 1 is movedfrom the upper toward the lower terminal of the resistance R, the volumecontrol is at first predominantly by virtue of decrease of positive biasupon the screen grid, and during the latter part of the downwardmovement, of the contact 1 the further volume reduction is predominantlydue to reduction of signal-representing voltage impressed upon the inputof the tube V.

In brief, the action is such that the amplification factor of the'tube Vis immediately reduced with resultant reduction in amplification due tothe first part of the downward movement of the brush 1, and this actioncontinues throughout the range of possible movement. Simultaneously theradio frequency shuntingaction of the adjustable resistance R,effectively in shunt to the primary P, is'at first, however, slight orgradual, but increases rapidly as the amplification factor of the tube Vis further reduced by reduction of the potential of the screen grid s.

it is apparent from the foregoing that the same electrical device ormeans accomplishes both functions 'of control of screen grid 'poten--tial and control of magnitude of voltage impressed upon the inputcircuit of the amplifier tube; amplification is varied simultaneouslywith diversion of input of signal energy by one and the same electricaldevice.

Fig. 2 is a diagram of a superheterodyne radio receiving system inwhich, between the antenna or absorption structure A and the first radiofrequency amplifier tube V1, of the screen grid type, is a preselectorsystem 4 comprising a plurality of cascaded circuits tunable to any ofthe frequencies within a range, such as that prevailing in presentbroadcasting practice. The plate circuit of the screen grid amplifier Vl is coupled through suitable coupling means including the transformerT1, whose secondary is tunable by the variable condenser-C1, tothe'input circuit of the first detector tube D1, of the screen gridtype.

O is a vacuum tube utilized as a local oscillator for producingoscillations of a frequency difi'erent from those representing thereceived signals, speech or music, to produce therewith in the inputcircuit of detector Dl beats of preferably constant and lower orintermediate radio frequency. The output of the detector D1 is coupledto the input of the intermediate freuency amplifier tube V2, of thescreen grid type, whose output in turn is" coupled to the iii-- put ofthe second detector tube D2. These two last mentioned couplings arepreferably fixedly tuned to the constant'or fixed intermediatefrequency. The output of the detector D2 is suitably coupled to theinput of the audio frequency amplifier V3 whose output is suitablycoupled to the push-pull amplifiers at whose output, amplified audiofrequency current, is de-- 'livered through a socket 5 to a loudspeaker,

such as an electro-dynamic loud speaker, whose voice coil connects withthe output of the tubes V4 through the socket 5 through which lattercurrent is delivered also to the field coil of the speaker.

' The power supply 6 is of any suitable type, and is here represented ascomprising a rectifierfilter, well understood in the art. My inventionis applied to the system of Fig. 2

generally'in accordance with the principles illustrated by Fig. 1.

Between the positive terminal 2 of the B source or power supply 6 andearth or ground E to which the negative terminal of the power supply isconnected, are serially connected the resistances R2, R3, R4 and'RSthrough which uni-directional current from the B source 6 continuouslyflows While the set is in operation. 7 These resistances, or anysuitable one thereof, as R3, may be considered in association with itsadjustable contact or slider 1 an adjustable resistance or apotentiometer. Between one of the. resistance R3 and the adjacent end ofthe resistance R4 is included a radio frequency choke coil 3 whichprevents radio frequency si nalrepresenting current from flowing throughresistances R4 and R5 to ground E. The choice coil offers high impedanceto radio frequency I currents but permits the direct current from the Bsource 6 readily to flow through all of the resistances mentioned.

j Sincethe contact 1 does not engage or move along the resistance R2,that resistance serves to limit the maximum positive voltage which maybe impressed upon the screen or shield grids s of the tubes V1, D1 andV2, all of which grids are connected to the contact 1 through theconductor '7. The resistances R4 and R5 to- 5 gether smilarly limit theminimum positive potential which may be applied to the same screen gridss of the three tubes aforesaid. ,The conductor 8 impresses upon thecontrol grids g of the tubes V1 and V a fixed or constant negativepotential or bias of a magnitude determined by the resistance R5.

The resistance R3 is in effect a potentiometer which permits byadjustment of the slider or brush 1 variation of the positive grid biasapplied to the screen grids s of the tubes V1, D1 and V2; adjustment ofthe slider 1 determines the amplification factors and the amplificationeffected by the tubes in question, movement of the slider 1 from lefttoward the right reducing volume by reduction of-amplification. Thevariable portion of the resistance R3 between the slider 1 and the point9 determines the shunting effect of that variable portion of theresistance 'to divert radio frequency energy from, or reduce theamountthereof impressed upon, the primary P of the coupling transformerT1, by virtue of connection of the point 9 throughconductor 10 to theupper terminal of the primary P whose lower terminal connects throughthe condenser K4 to ground E and thence through condenser K5 andconductor. 7 to the movable contact 1. Movement of the contact 1 fromleft toward the right thereby increases the shunting effect upon theprimary P and therefore reduces the radio'frequency signal-representingenergy impressed from the output of the tube V1 upon the input of thedetector tube D1. Each of condensers K4 and K5 has a capacity of theorder of .1 microfarad; in any event each of these condensers offersvery low reaotance to the radio frequency current. The condenser K4serves to prevent short circuit of the direct current from the B source6' flowing through the resistances R2 to R5 inclusive.

Simultaneously with reduction of amplification by movement of slider lfrom left toward the right on resistance R3, the shunting effect uponthe primary P increases, whereby the volume of reproduction by the loudspeaker is.

controlled by the conjoint action of the two effects which, however, areproduced by 'one and the same electrical instrument as a variableresistance, a potentiometer, or any equivalent means.

As in the case of Fig. l, the reduction of amplification by movement ofthe slider 1 operates immediately upon movement of the slider from theleft end of the resistance R3 and continues throughout its possiblerange of movement, further to reduce the amplification, which, however,cannot be'reduced. substantially to zero because the positive potentialof the screen grids may not be reducedbelow a certain magnitude asdetermined by the potential difference across the resistancesR4 and R5in series. Simultaneously, the reduction of radio frequency input, orthe diversion of radio frequency from the input of a tube, or from .acoupling between tubes, is effected, first at very low rate, adjacentthe left end of the resistance R3, and then at very rapidly increasingrate as the slider lapproaches the right end of resistance R3.

By .way of example merely it may be stated senting energy, 1

"2. In a radio receiver, a thermionic tube of said resistance in a pathwhose resistance determines the transfer of radio frequency signalthatwhen the voltage of the B source 6 is of the order of 150 to 200 voltsthe resistance R2 may be 20,000 to130,000-. ohms; R3, 50,000 to 100,000ohms; R4, 10,000 to 15,000 ohms; and R5 about 200 ohms. Theseproportions have been found to give suitable potentials as impressedupon the screen grid s of the tubes V1, D1 and V2,'when' of the presenttype [IX-224; and for effecting by resistance R5a constant or fixednegative bias of substantially three volts upon the control grids of thetubes V1 and V2.

What I claim is: I

1. In a radio receiver, a thermionic tube of the screen grid type, aresistance,.means for passing uni-directional current therethrough,means for varying the amount of resistance between a point and aconnection to the screen grid of said" tube for varying the potentialthereof, and connections-for including the resistance between said pointand connection in a signal transfer system of the receiver forsimultaneously varying the transfer. of signal-reprethe screen gridtype, a resistance, means for passing uni-directional current throughsaid resistance, means for effecting connection wi'th saidresistance ata plurality of points thereon and in circuit with the screen grid ofsaidtube for varying the potential thereof, and connections forincluding a portion of said resistance so varied in a path traversed bythe signal energy for varying the transfer of said energy in saidsystem. 7

3. In a radio receiving system, a thermionic tube of the screen gridtype, a resistance, a source of current for the anode circuit of saidtube passing current through said resistance, means for effectingconnection with said resistance at a plurality of points thereon and incircuit with the screen grid of said tube] for varying the potentialthereof, and connections for including a portion of said resistance sovaried in a path whose resistance determines the transfer ofsignal-representing energy in said system.

quency amplifier tube of the screen grid type, a resistance, means forpassing uni-directional current through said resistance, a contactmovable along'said resistance for varying the po-' tential of the screengrid of said tube, andcon nections for including the variable portion ofrepresenting energy in said system.

5. 111 2. radio receiving'system, a radio Ire quency amplifier tube ofthe screen grid type, a

resistance for diversion from saidtube of radio frequencysignal-representingenergy, means for passing uni-directionalcurrent'through said resistance, and a-contact movable along said rersistance for simultaneously varying the diversion aforesaid from, andthe potential of the screen grid of, said tube, for simultaneouslyvarying the volume of reproduction in the same senses and cumulativelythroughout the range of movement of said contact. l V

6. A radio receiving system comprising a plurality of thermionic tubesin cascade, at least one of which is of the screengrid type,a-resistance, means for passinguni-directional current therethrough,means for effecting connection with said resistance'at a" plurality ofpoints '.thereon and in circuit with the screen grid of at least oneofsaid tubes: for varyingthe potential thereof to -vary the volume ofreproduction,. and means for 'efiecting simultaneous Cumulative volumevariation comprising-connections for including a portion of saidresistance so varied in an inter-tube coupling system for varying thetransfer .ofsignal-representing. energy from said one of said tubes toanother tube of said system- 7. In a radio receiving systenn a detectorof the screen grid type, a resistance, means for passing uni-directionalcurrent through said resistance, means for effecting connection withsaid resistance at a plurality of points thereon and in circuit with thescreen grid 'of'said detector for varying the potential thereof, andconnections for. including a portion of said resistance so variedin apath traversed by signal energy for varyinggthe transfer thereof in saidsystem.

8. In a radio receiving system, an amplifier tube of the screen gridtype, in. a later stage a a resi stance, means for passinguni-directional current through said resistance, means for effectingconnection with said resistance ata plurality of points thereon andincircuit: withjthe screengrids of said tubes for varying the potentialsthereof,; and connections for including a portion of said resistance, sovaried in a path whose resistance determines the transfer ofsignal-representing energy in said system.

10. In a heterodyne receiving system, a radio frequency amplifier tubeofv the screen gridtype, an oscillator; a detector tube of the screengrid type, means for coupling-the output of saidfirst named-tubetotheinput of said detectortube, a resistance, means for passinguni-directional current through said resistance, means for effectingconnection with said resistance at aipluralityof points thereon and incircuitwith the screen grids of said tubes for varying the potene -tialsthereof, and connections for including a portion of said resistance sovaried in circuit with said coupling means for-varying the trans fer ofsignal-representing energy. v

v 11. In a superheterodyne receiving system, a radio frequencyvamplifiertube; of the screen grid type, an oscillator, a first detectortube of the screenggrid type,ran intermediate frequency amplifier of thescreen grid-type, a resistance means for passing uni-directional currentthrough said resistance, means for effecting con necticn with-saidresistancaat' a plurality of points thereon and in circuitwiththe screengrids of said tubes. for varying the potentials thereof, and connectionsfor including a portion of said resistance so varied in-a pathwhoseresistancedetermines thetransfer of signal-representing energy in saidsystem. i,

12. In a radio receiving system comprising. one or more amplifyingtubes. of the screen grid type, the method of, controlling the ,volumeof reproduction which comprises varying a resistance to vary-the screengrid potential of at least one of said tubes to vary its amplification,and

simultaneously, by the same variation of said resistance, varying thetransfer of signal-,representing energy. 7

13. In a radio receiving system comprising one ormore tubes of thescreen grid type, a coupling for transferring signal-representingenergy, and a resistance for affecting said coupling in its transfer ofsaid energy, the method of controlling the volume of reproduction whichvcomprises passing uni-directional current through said resistance,adjusting a contact along said resistance to .vary the screen gridpotential of at least one of said tubes to effect one component of thevolume control varying in the same sense throughout adjustment of saidcontact, and simultaneously by adjustment said resistance by saidcontact varying the transfer of signal-representing energy by saidcoupling to effect another component of the volume control. varying inthe. same sense with said first named component. 14. In a radioreceiving system, a thermionic tube of the screen grid type, a couplingfor transferring signal-representing energy, a ,resistance in shunt tosaid coupling and in circuit with the screen grid of said tube, meansfor passing unidirectional current through said'resistance, and a,contact adjustable along said resistance for, varying the potential ofthe screen said tube to. effectlone component of a volume controlcarying in the same sense throughout said adjustment, and simultaneouslyto vary the transfer of signal-representing energy effected by saidcoupling to effect another component ofthe volume control varying in thesame sense, with said firstqnamed component.

l5.'In a radio receiving system, a thermionic tube of the screen gridtype, a magnetic -cou=- pling for transferring signal-representingenergy, a resistance in circuit with the screen grid of said tube,capacity in series with said resistance inshunt with said coupling,meansfor passing uni-directional current through said resistance, and acontact adjustable along said resistance for varying the potential ofthe screen gridof said tube to effect one component of a volume controlvarying in the same sense throughout said adjustment, and simultaneouslyto vary the transfer of signal-representing energy effected by saidcoupling to effect another component of thevolume control varying in thesame sense with said first-named component.

'16. In a radio receiving system, a thermionic tubepf the screen gridtype, ascurce of unidirectional current, a resistance traversed bycurrent"from said source, a radiofrequency choke coil connectingsections of said resistance for excluding radio frequency current fromone sectionthereof, a coupling for transferring signal-representingenergy, a connection to said one of. said sections of said resistancefor biasing a control grid of a tube of said system, and means forcontrolling the volume of reproduction comprising a contact movablealonganother of .said sections of said resistance to vary the potential ofthe-screen grid of said tube'for effecting.one...component of the volumecontrol, and connections to said coupling for causing said adjustment ofsaid contact along said other of SAMUEL w. PLACE,

CERTIFICATE 0F (IQRRECTION.

Patent No. 1,926,173. September 12, 1933.

SAMUEL W. PLACE.

it is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 1,line 72, for "treminal" read terminal; page 4, line 60, claim 11, inserta comma after "resistance"; and line 106. claim 14, for "carying" readvarying; and that the said Letters Patent should be read with thesecorrections therein that the same may conform to the record of the casein the Patent Office.

Sign d and sealed this 21st day of November, A. i). 1933.

F. M. Hopkins (Seal) Acting Commissioner of Patents.

